I hesitate to get involved in these discussions, especially since I'm new here, but since this peeked my interest I'd like to share.
As for the second coming, that's already happened. It was prophesied that Jesus would sit at the right hand of God until he placed his enemies at his feet. Ps.110:1.
The first thing Jesus did when he came in to power was to kick out Satan and his demons from heaven forever. They could no longer go back and forth. This enraged Satan and it's been "Woe for the earth" (Rev. 12:12) ever since. This took place in 1914. We can figure this date by using Bible chronology and by what took place in 1914. WWI. Never had the entire world been at war. It was so horrendous and unheard of that they even named it a World War.
As for Matt. 16:28, Jesus took Peter, James, and John up into the mountain and was transfigured. A foregleam of his coming in to Kingdom Power. So we can see that his words were right on the mark. Peter, James and John were Not dead, and they saw the forgleam of Jesus coming in to power.
As for the "day of the Lord", this is something completely different from the second coming. "The day of the Lord" is God's war at Armageddon to destroy all evil from the earth.
As for your "six years left", are you alluding to the Mayan calender?
http://www.crawford2000.co.uk/maya.htm
hoping the link works